Hi James. Sorry for my late reply. I know you have solved this but just in case this is handy to you, or someone else…
david_blanchard and I have also sometimes had problems with using an A1243 keyboard. See previous thread here: Wired USB-A keyboard issue. In my case, adding a USB extension cable resolved the issue. But david_blanchard needed to remove an extension cable to get it to work (!). There are other suggestions at the Stack Exchange question I linked to in that thread, including plugging a USB memory stick into the keyboard, to increase the current draw.